Particle beam devices have already been used for a long time for obtaining knowledge in respect of the properties and the behavior of objects (also referred to as samples below) under certain conditions. An electron beam device, in particular a scanning electron microscope (also referred to as SEM below) or a transmission electron microscope (also referred to as TEM below), is one of these particle beam devices.
In the case of an SEM, an electron beam (also referred to as primary electron beam below) is generated using a beam generator and focused on a sample to be examined by a beam guidance system, in particular by an objective lens. Using a deflection apparatus, the primary electron beam is guided over a surface of the sample to be examined in a raster-like manner. Here, the primary electron beam electrons interact with the material of the sample to be examined. Interaction particles, in particular, are generated as a result of the interaction. By way of example, electrons (so-called secondary electrons) are emitted from the surface of the sample to be examined and primary electron beam electrons (so-called backscattered electrons) are scattered back. The secondary electrons and the backscattered electrons are detected and used for generating an image. Thus, an image of the surface of the sample to be examined is obtained.
Furthermore, the prior art has disclosed the practice of using combination devices for examining and/or processing samples, in which both electrons and ions may be guided onto a sample to be examined and/or to be processed. By way of example, the practice of additionally equipping an SEM with an ion beam column is known. Ions which are used for processing a sample (e.g. ablating a surface of the sample or applying material to the sample) or else for imaging are generated using an ion beam generator arranged in the ion beam column. In this case, the SEM serves, in particular, for observing the processing (i.e. a preparation of the sample), but also for the further examination of the unprepared and/or prepared sample.
By way of example, using the aforementioned combination device, it is possible to produce, in the form of a TEM lamella, a sample to be examined (i.e. to be analyzed). The TEM lamella comprises a region which can be examined in more detail using a TEM. By way of example, this region is referred to as a target region. By way of example, in order to produce the TEM lamella, the ion beam is used to ablate regions of the sample arranged around the target region such that the TEM lamella, which then comprises the target region, is exposed.
In the TEM, a primary electron beam, which extends along an optical axis of the TEM, passes through the target region of the TEM lamella. By way of example, electrons of the primary electron beam transmitted (i.e. passed) through the target region of the TEM lamella are detected using a detector. The detector provides detection signals which are evaluated and used for the analysis of the target region.
In order to be able to obtain good transmission of the primary electron beam electrons through the target region, it is desirable for the TEM lamella, at least in the target region, to have a substantially identical extent—to be precise, as seen in the beam direction of the primary electron beam and/or in the direction of the optical axis of the TEM. This promotes sufficiently good transmission of the primary electron beam electrons through the target region. Expressed differently, the TEM lamella should, at least in the target region, have an embodiment with a uniform thickness in the beam direction of the primary electron beam and/or in the direction of the optical axis of the TEM.
In order, firstly, to obtain a uniform extent of the TEM lamella in the beam direction of the primary electron beam (or in the direction of the optical axis of the TEM) and, secondly, to embody the TEM lamella in such a way that the TEM lamella sufficiently encompasses the target region, the prior art has disclosed a method by which the TEM lamella can be produced in an aforementioned combination device. This will now be explained in more detail with reference to FIG. 1. Initially, the SEM is used to identify a target region ZB, to be examined, on a surface of a sample O to be examined. Now, a scan region RB on the surface of the sample O is selected at a selectable distance from the target region ZB, for example at a distance of a few micrometers. The scan region RB is composed of a multiplicity of scan lines which, for example, are arranged parallel to one another. Each scan line comprises a multiplicity of scanning points P. In an exemplary manner, FIG. 1 shows three scan lines of the scan region RB, namely a first scan line RZ1, a second scan line RZ2 and a third scan line RZ3.
The scan region RB is now processed using the ion beam. This is observed using the SEM. In the exemplary embodiment depicted in FIG. 1, the scan region RB is exposed using the ion beam. In other words, the material of the sample O encompassed by the scan region RB is ablated. Ablating material is also known by the specialist term “milling”. The material is ablated in such a way that the ion beam is firstly guided along the arrow direction PA to each individual scan line RZ1 to RZ3 and is secondly guided in succession along the arrow direction PB to each scanning point P along each scan line RZ1 to RZ3. The scan region RB approaches the target region ZB as a result of the continued movement of the ion beam in the arrow direction PA and the ablation of the material as explained above. Therefore, it is possible to expose a TEM lamella made of the material of the sample O by ablating material around the target region ZB, e.g. to release the TEM lamella from the sample O and e.g. to examine it in more detail in a TEM.
From observing FIG. 1, it becomes clear that the scan region RB would not be aligned parallel to the target region ZB in the case of continued movement in the arrow direction PA. However, said parallel alignment is desired so as to obtain an extent of the TEM lamella, at least in the target region ZB, which is as uniform as possible. In order to align the scan region RB parallel to the target region ZB, the practice of rotating the scan region RB about an axis 100 has been disclosed. The axis 100 is fixedly predetermined and passes through a point on the surface of the sample O. The axis 100 corresponds to the optical axis of the ion beam column in the combination device. The scan region RB is then rotated about the axis 100 by a so-called scan rotation of the ion beam. Here, a scanning direction is rotated by virtue of two deflection elements of the ion beam column, which are provided for deflecting the ion beam, being actuated in a targeted manner. Thus, provision is made for a first deflection element for deflecting the ion beam in an X-direction to be, in addition to a control voltage for the X-direction, actuated by a component of the control voltage for a Y-direction. Furthermore, a second deflection element for deflecting the ion beam in a Y-direction is, in addition to a control voltage for the Y-direction, actuated by a component of the control voltage for the X-direction. Here, the components of the control voltages on the respective deflection system are usually determined taking into account the angle of rotation a according to the sine/cosine method. Here, the control voltage for the first deflection system V1 is calculated from the control voltage for the X-direction Vx and from the control voltage for the Y-direction Vy according to V1=Vx cos α−Vy sin α. The control voltage for the second deflection system V2 is calculated from the control voltage for the Y-direction Vy and from the control voltage for the X-direction Vx according to V2=Vx sin α+Vy cos α. If the scan region RB is at a distance from the axis 100 (cf. FIG. 1), the scan region RB of the ion beam moves away from its original position when carrying out the scan rotation and possibly also wanders out of the observation region of the SEM. Therefore, the ion beam is initially guided back toward the scan region RB again. This is obtained using a so-called “beam shift”, in which the ion beam is guided back to the original scan region RB again by translational movements.
This known method is complicated due to the two possible adjustment stages, namely, firstly, the scan rotation and, secondly, the beam shift. It is therefore desirable to specify a method by which, in particular, a parallel approach of the scan region RB to the target region ZB is possible in a simple manner and by which the TEM lamella can be embodied with uniform thickness, particularly in the target region ZB.
In respect of the further prior art, reference is made to U.S. Pat. No. 8,350,237 B2, which is incorporated herein by reference, in which a method for automated ablation of material of an object is described.
Accordingly, it would be desirable to specify a method for processing and/or observing an object, which method enables, in a simple manner, the generation of uniformly thick objects and the rotation of a scan region over the surface of the object in a simple manner.